一段文句
The criteria – a route to send defensive supplies to northern military bases
should mainland US or Canada be attacked, far enough inland that enemy planes
couldn't reach it – made the proposed route starting from Dawson Creek the
top contender.
出处
https://reurl.cc/NpxrAp
请教这边should mainland US or Canada be attacked该怎么解释?
是修饰military bases吗?
相关的文法应用该怎么参考?

should这里跟if差不多意思。查字典应该可以查到这种should的用法。

if mainland US or Canada should be attacked倒装句，指“如果……发生的话”

should had 等助动词假设语气可以倒装这种用法会话也会用到喔 建议学起来

had, should, were

谢谢各位